While I agree that more info is better, his question is a simple one and can be answered without knowing what transmission he has. He asked if the output shaft of a transmission can be changed to make a long shaft transmission fit where a short shaft transmission used to reside. The answer is yes, but it isn't worth doing. You will have to disassemble most of the transmission to do it. You will be much better off finding another transmission that is the same as the current one. Unless you are a veteran at rebuilding transmissions, it will take far more effort educating yourself on the procedure. In addition, the uncertainty of doing it the first time and the potential problems far outweigh the expense of buying another unit. Find the right one in a pull-it-yourself yard or on craigslist. It will be well worth the time and frustration you save.